BIOLOGY Volume 1 - A Guide to General Biology - 2004

8. HETEROTROPHIC NUTRITION

8.9. Malnutrition

8.9.3. Starvation and General Undernutrition

To survive, humans require a continuous supply of energy. During starvation, energy reserves are progressively depleted, which can eventually lead to death. Glycogen stored in The Liver and Muscles is consumed first. In the absence of food, this source sustains the body with energy for approximately half a day. Next, fat reserves are mobilized. In an average person, fat stores can supply the body with energy for up to 50 days. Fat is broken down in the liver to form Fatty acids, which replace glucose in cellular Respiration. However, fatty acids can produce ketones, which tend to accumulate in the Blood, causing a condition known as Ketosis that leads to blood acidification. One of the resulting ketones is acetone. It is synthesized in small amounts, yet it imparts a characteristic odor to the breath, making ketosis easily recognizable.

During the first week of starvation, Muscle protein is also utilized as an energy source. It is converted into glucose through a process called Gluconeogenesis. Protein utilization then practically ceases until fat reserves are exhausted. Protein breakdown resumes in the final stages of starvation just before death (Fig. 8.29). To meet energy demands, the body begins to break down its own Tissues, such as muscles. Death typically occurs when roughly half of the body's Proteins have been depleted. Total starvation generally leads to death within 40 to 60 days.

Children who have been deprived of adequate, nutritious food for extended periods exhibit stunted growth and low body weight. They may develop severe wasting (marasmus; Section 8.9.4). It is only relatively recently that developed countries have successfully addressed Structure/149.html">The problem of undernutrition, whereas developing nations still face numerous challenges in ensuring an adequate food supply for their populations.

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Fig. 8.29. The Effect of starvation on nutrient reserves in The Human Body. (From Textbook of Medical Physiology, 9th ed., A. C. Guyton, J. E. Hall (1996), W. B. Saunders a. Co.)